Slow rewarming improves jugular venous oxygen saturation during rewarming

Depth of anesthesia, temperature, and postoperative delirium in children and adolescents undergoing cardiac surgery

BACKGROUND

After pediatric cardiosurgical interventions, postoperative delirium can occur, which can be associated with undesirable consequences during and after the hospital stay. It is therefore important to avoid any factors causing delirium as far as possible. Electroencephalogram (EEG) monitoring can be used during anesthesia to individually adjust dosages of hypnotically acting drugs. It is necessary to gain knowledge about the relationship between intraoperative EEG and postoperative delirium in children.

METHODS

In a dataset comprising 89 children (53 male, 36 female; median age: 0.99 (interquartile range: 0.51, 4.89) years) undergoing cardiac surgery involving use of a heart-lung machine, relationships between depth of anesthesia as measured by EEG (EEG index: Narcotrend Index (NI)), sevoflurane dosage, and body temperature were analyzed. A Cornell Assessment of Pediatric Delirium (CAP-D) score ≥ 9 indicated delirium.

RESULTS

The EEG could be used in patients of all age groups for patient monitoring during anesthesia. In the context of induced hypothermia, EEG monitoring supported individually adjusted sevoflurane dosing. The NI was significantly correlated with the body temperature; decreasing temperature was accompanied by a decreasing NI. A CAP-D score ≥ 9 was documented in 61 patients (68.5%); 28 patients (31.5%) had a CAP-D < 9. Delirious patients with an intubation time ≤ 24 h showed a moderate negative correlation between minimum NI (NImin) and CAP-D (rho = -0.41, 95% CI: -0.70 - -0.01, p = 0.046), i.e., CAP-D decreased with increasing NImin. In the analysis of all patients' data, NImin and CAP-D showed a weak negative correlation (rho = -0.21, 95% CI: -0.40 - 0.01, p = 0.064). On average, the youngest patients had the highest CAP-D scores (p = 0.002). Patients with burst suppression / suppression EEG had a longer median intubation time in the intensive care unit than patients without such EEG (p = 0.023). There was no relationship between minimum temperature and CAP-D score.

CONCLUSIONS

The EEG can be used to individually adjust sevoflurane dosing during hypothermia. Of the patients extubated within 24 h and classified as delirious, patients with deeper levels of anesthesia had more severe delirium symptoms than patients with lighter levels of anesthesia.

The effect of rewarming on hemodynamic parameters and arterial blood gases of patients after open-heart surgery: A randomized controlled trial

INTRODUCTION

Hypothermia after open-heart surgery can have potential side effects for patients.

AIM

This study aimed to examine the effects of rewarming on patients' hemodynamic and arterial blood gases parameters after open-heart surgery.

METHODS

This randomized controlled trial was performed in 2019 on 80 patients undergoing open-heart surgery at Tehran Heart Center, Iran. The subjects were consecutively recruited and randomly assigned to an intervention group (n=40) and a control group (n=40). After the surgery, the intervention group was warmed with an electric warming mattress while the control group warmed using a simple hospital blanket. The hemodynamic parameters of the two groups were measured 6 times and arterial blood gas was measured 3 times. Data were analyzed by independent samples t and Chi-squared tests, and repeated measures analysis.

RESULTS

Before the intervention, the two groups did not significantly differ in terms of hemodynamic and blood gas parameters. However, the two groups were significantly different in the mean heart rate, systolic blood pressure, diastolic blood pressure, mean arterial blood pressure, temperature, right and left lung drainage in the first half-hour, and the first to fourth hours after the intervention (p < 0.05). Furthermore, there was a significant difference between the mean arterial oxygen pressure of the two groups during and after rewarming (P <0.05).

CONCLUSION

Rewarming of patients after open-heart surgery can significantly affect hemodynamic and arterial blood gas parameters. Therefore, rewarming methods can be used safely to improve the patients' hemodynamic parameters after open-heart surgery.

Extracorporeal Life Support in Accidental Hypothermia with Cardiac Arrest-A Narrative Review

Severely hypothermic patients, especially suffering cardiac arrest, require highly specialized treatment. The most common problems affecting the recognition and treatment seem to be awareness, logistics, and proper planning. In severe hypothermia, pathophysiologic changes occur in the cardiovascular system leading to dysrhythmias, decreased cardiac output, decreased central nervous system electrical activity, cold diuresis, and noncardiogenic pulmonary edema. Cardiac arrest, multiple organ dysfunction, and refractory vasoplegia are indicative of profound hypothermia. The aim of these narrative reviews is to describe the peculiar pathophysiology of patients suffering cardiac arrest from accidental hypothermia. We describe the good chances of neurologic recovery in certain circumstances, even in patients presenting with unwitnessed cardiac arrest, asystole, and the absence of bystander cardiopulmonary resuscitation. Guidance on patient selection, prognostication, and treatment, including extracorporeal life support, is given.

Targeted temperature management at 33 degrees Celsius in patients with high-grade aneurysmal subarachnoid hemorrhage: a protocol for a multicenter randomized controlled study

Background

Studies on the use of therapeutic hypothermia (TH) to improve the outcome of high-grade aneurysmal subarachnoid hemorrhage (aSAH), show promising, though conflicting results because of the lack of high-quality trials. The aim of this study is to evaluate the safety and efficacy of TH (maintaining bladder temperature at 33 °C for ≥72 h) to treat patients with high-grade aSAH (Hunt-Hess grade IV-V).

Methods

A multicenter, randomized, controlled clinical trial will be conducted for October 2020 to September 2024 involving 10 clinics. Patients who meet the inclusion criteria will be randomized 1:1 to a TH group and a normothermia group. The trial will enroll 96 participants in TH group and normothermia one, respectively. The trial was registered with ClinicalTrials.gov (NCT03442608) on February 22, 2018. Following conventional treatment for aSAH, patients will undergo either TH for at least 72 h or normothermia. The primary endpoint is the Glasgow outcome scale at 6 months after bleeding. The secondary endpoints are: (I) mortality at 6 months after bleeding; (II) intracranial pressure; (III) intensive care unit stay; and (IV) hospital stay. The safety endpoints include neurological, infectious, intestinal, circulatory, coagulation, and bleeding complications, electrolyte disorders, and other complications.

Discussion

If the study hypothesis is confirmed, TH at 33 °C in patients with high-grade aSAH may become a promising treatment strategy for improving 6-month outcome.

Trial registration

The trial has been registered at ClinicalTrials.gov (ID: NCT03442608).

The "Ice Age" in Cardiac Surgery: Evolution of the "Siberian" Method of Brain Protection During Deep Hypothermic Perfusionless Circulatory Arrest

Deep hypothermic perfusionless circulatory arrest was the first practical neuroprotective technique used for open-heart surgery. It was refined at the Novosibirsk Medical Research Center in Siberia and was actively used from the mid-1950s until 2001.This review describes the development of this technique and its contribution to our understanding of the dynamic changes in human physiology during induced hypothermia for circulatory arrest without extracorporeal perfusion. Deep hypothermic perfusionless circulatory arrest was an important stepping stone in the development of modern approaches in neuroprotection and monitoring during cardiac surgery.

Pilot study on a rewarming rate of 0.15°C/hr versus 0.25°C/hr and outcomes in post cardiac arrest patients

Objective

Cerebral hemodynamic and metabolic changes may occur during the rewarming phase of targeted temperature management in post cardiac arrest patients. Yet, studies on different rewarming rates and patient outcomes are limited. This study aimed to investigate post cardiac arrest patients who were rewarmed with different rewarming rates after 24 hours of hypothermia and the association of these rates to the neurologic outcomes.

Methods

This study retrospectively investigated post cardiac arrest patients treated with targeted temperature management and rewarmed with rewarming rates of 0.15°C/hr and 0.25°C/hr. The association of the rewarming rate with poor neurologic outcomes (cerebral performance category score, 3 to 5) was investigated.

Results

A total of 71 patients were analyzed (0.15°C/hr, n=36; 0.25°C/hr, n=35). In the comparison between 0.15°C/hr and 0.25°C/hr, the poor neurologic outcome did not significantly differ (24 [66.7%] vs. 25 [71.4%], respectively; P=0.66). In the multivariate analysis, the rewarming rate of 0.15°C/hr was not associated with the 1-month neurologic outcome improvement (odds ratio, 0.54; 95% confidence interval, 0.16 to 1.69; P=0.28).

Conclusion

The rewarming rates of 0.15°C/hr and 0.25°C/hr were not associated with the neurologic outcome difference in post cardiac arrest patients.

Insulin resistance plays a potential role in postoperative cognitive dysfunction in patients following cardiac valve surgery

Severe insulin resistance (IR) promotes the development of Alzheimer disease. IR and postoperative cognitive dysfunction (POCD) are a common complication during the cardiac perioperative period. The authors hypothesized that IR of individuals with cardiac valve surgery would have increased the risk of POCD. The purpose of the study was to analyze the association of IR and POCD after cardiac valve surgery. Total 131 patients who underwent valve replacement via cardiopulmonary bypass (CPB) were included. Cognitive function was assessed by a series of neuropsychological measurements at 1day before and 7days after the surgery. 40 healthy volunteers as the control group also completed the neuropsychological assessment at the same time point. POCD was identified using the "Z score" method. Fasting blood glucose and insulin levels were detected before anesthesia and at 6h and 7days post-operation. Additionally serum levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α) were measured at 6h post-operation. The insulin resistance index was calculated by "homeostasis model assessment 2" (HOMA2) software. The relationship between IR and POCD or TNF-α, IL-6 was then analyzed. At 7days after surgery, the incidence of POCD was 43.8%. The levels of HOMA2-IR in patients with POCD were significantly higher than those of patients without POCD at 6h and 7days after operation (P<0.05).The levels of serum IL-6 and TNF- α were positively correlated with HOMA2-IR value at 6h after operation (RIL-6=0.426, P<0.01; RTNF-a=0.381, P<0.01). POCD was correlated with the patients' education age (OR=1.062), CPB time (OR=1.018), self-rating depression scale (SDS) score after operation (OR=1.082), HOMA2-IR at 6h (OR=1.110) and 7days (OR=13.762) after operation, IL-6 (OR=1.036) and TNF-α (OR=1.039) at 6h after operation. Our study suggests that IR is correlated with the incidence of POCD and the increase of inflammatory factors.

What is the value of regional cerebral saturation in post-cardiac arrest patients? A prospective observational study

Background

The aim of this study was to elucidate the possible role of cerebral saturation monitoring in the post-cardiac arrest setting.

Methods

Cerebral tissue saturation (SctO₂) was measured in 107 successfully resuscitated out-of-hospital cardiac arrest patients for 48 hours between 2011 and 2015. All patients were treated with targeted temperature management, 24 hours at 33 °C and rewarming at 0.3 °C per hour. A threshold analysis was performed as well as a linear mixed models analysis for continuous SctO₂ data to compare the relation between SctO₂ and favorable (cerebral performance category (CPC) 1–2) and unfavorable outcome (CPC 3–4–5) at 180 days post-cardiac arrest in OHCA patients.

Results

Of the 107 patients, 50 (47 %) had a favorable neurological outcome at 180 days post-cardiac arrest. Mean SctO₂ over 48 hours was 68 % ± 4 in patients with a favorable outcome compared to 66 % ± 5 for patients with an unfavorable outcome (p = 0.035). No reliable SctO₂ threshold was able to predict favorable neurological outcome. A significant different course of SctO₂ was observed, represented by a logarithmic and linear course of SctO₂ in patients with favorable outcome and unfavorable outcome, respectively (p < 0.001). During the rewarming phase, significant higher SctO₂ values were observed in patients with a favorable neurological outcome (p = 0.046).

Conclusions

This study represents the largest post-resuscitation cohort evaluated using NIRS technology, including a sizeable cohort of balloon-assisted patients. Although a significant difference was observed in the overall course of SctO₂ between OHCA patients with a favorable and unfavorable outcome, the margin was too small to likely represent functional outcome differentiation based on SctO₂ alone. As such, these results given such methodology as performed in this study suggest that NIRS is insufficient by itself to serve in outcome prognostication, but there may remain benefit when incorporated into a multi-neuromonitoring bedside assessment algorithm.

Risk Factors Associated with Cognitive Decline after Cardiac Surgery: A Systematic Review

Modern day cardiac surgery evolved upon the advent of cardiopulmonary bypass machines (CPB) in the 1950s. Following this development, cardiac surgery in recent years has improved significantly. Despite such advances and the introduction of new technologies, neurological sequelae after cardiac surgery still exist. Ischaemic stroke, delirium, and cognitive impairment cause significant morbidity and mortality and unfortunately remain common complications. Postoperative cognitive decline (POCD) is believed to be associated with the presence of new ischaemic lesions originating from emboli entering the cerebral circulation during surgery. Cardiopulmonary bypass was thought to be the reason of POCD, but randomised controlled trials comparing with off-pump surgery show contradictory results. Attention has now turned to the growing evidence that perioperative risk factors, as well as patient-related risk factors, play an important role in early and late POCD. Clearly, identifying the mechanism of POCD is challenging. The purpose of this systematic review is to discuss the literature that has investigated patient and perioperative risk factors to better understand the magnitude of the risk factors associated with POCD after cardiac surgery.

The accuracy of a near-infrared spectroscopy cerebral oximetry device and its potential value for estimating jugular venous oxygen saturation

BACKGROUND

An intriguing potential clinical use of cerebral oximeter measurements (SctO2) is the ability to noninvasively estimate jugular bulb venous oxygen saturation (SjvO2). Our purpose in this study was to determine the accuracy of the FORE-SIGHT(®) (CAS Medical Systems, Branford, CT), which is calibrated to a weighted average of 70% (SjvO2) and 30% arterial saturation, for Food and Drug Administration pre-market approval 510(k) certification by adapting an industry standard protocol, ISO 9919:2005 (www.ISO.org) (used for pulse oximeters), and to evaluate the use of SctO2 and SpO2 measurements to noninvasively estimate jugular venous oxygen saturation (SnvO2).

METHODS

Paired blood gas samples from the radial artery and the jugular venous bulb were collected from 20 healthy volunteers undergoing progressive oxygen desaturation from 100% to 70%. The blood sample pairs were analyzed via co-oximetry and used to calculate the approximate mixed vascular cerebral blood oxygen saturation, or reference SctO2 values (refSctO2), during increasing hypoxia. These reference values were compared to bilateral FORE-SIGHT SctO2 values recorded simultaneously with the blood gas draws to determine its accuracy. Bilateral SctO2 and SpO2 measurements were then used to calculate SnvO2 values which were compared to SjvO2.

RESULTS

Two hundred forty-six arterial and 253 venous samples from 18 subjects were used in the analysis. The ipsilateral FORE-SIGHT SctO2 values showed a tolerance interval (TI) of [-10.72 to 10.90] and Lin concordance correlation coefficient (CCC) with standard error (SE) of 0.83 ± 0.073 with the refSctO2 values calculated using arterial and venous blood gases. The ipsilateral data had a CCC of 0.81 + 0.059 with TI of [-9.22 to 9.40] with overall bias of 0.09%, and amplitude of the root mean square of error after it was corrected with random effects analysis was 2.92%. The bias and variability values between the ipsilateral and the contralateral FORE-SIGHT SctO2 measurements varied from person to person. The SnvO2 calculated from the ipsilateral SctO2 and SpO2 data showed a CCC ± SE of 0.79 ± 0.088, TI = [-14.93 to 15.33], slope of 0.98, y-intercept of 1.14% with SjvO2 values with a bias of 0.20% and an Arms of 4.08%. The SnvO2 values calculated independently from contralateral forehead FORE-SIGHT SctO2 values were not as correlated with the SjvO2 values (contralateral side CCC + SE = 0.72 ± 0.118, TI = [-14.86 to 15.20], slope of 0.66, and y-intercept of 20.36%).

CONCLUSIONS

The FORE-SIGHT cerebral oximeter was able to estimate oxygen saturation within the tissues of the frontal lobe under conditions of normocapnia and varying degrees of hypoxia (with 95% confidence interval of [-5.60 to 5.78] with ipsilateral blood sample data). These findings from healthy volunteers also suggest that the use of the calculated SnvO2 derived from SctO2 and SpO2 values may be a reasonable noninvasive method of estimating SjvO2 and therefore global cerebral oxygen consumption in the clinical setting. Further laboratory and clinical research is required to define the clinical utility of near-infrared spectroscopy determination of SctO2 and SnvO2 in the operating room setting.

Effect of slow versus rapid rewarming on jugular bulb oxygen saturation in adult patients undergoing open heart surgery

BACKGROUND

A debate has appeared in the recent literature about the optimum rewarming strategy (slow vs. rapid) for the best brain function. This study was designed to compare the effect of slow versus rapid rewarming on jugular bulb oxygen saturation (SjO2) in adult patients undergoing open heart surgery.

MATERIALS AND METHODS

A total of 80 patients undergoing valve and adult congenital heart surgery were randomly allocated equally to rapid rewarming group 0.5 (0.136)°C/min and slow rewarming group 0.219 (0.055)°C/min in jugular bulb sampling was taken before, during and after surgery. Surgery was done at cardiopulmonary bypass (CPB) temperature of 28-30°C and rewarming was performed at the end of the surgical procedure.

RESULTS

CPB time, rewarming period were significantly longer in the slow rewarming group. Significant difference was observed in the number of the desaturated patients (SjO2 ≤ 50%) between the two groups; 14 (35%) in rapid rewarming versus 6 (15%) in the slow rewarming group; P = 0.035 by Fisher's exact test.

CONCLUSIONS

Slow rewarming could reduce the incidence of SjO2 desaturation during rewarming in adult patients undergoing open heart surgery.

The effects of the rate of postresuscitation rewarming following hypothermia on outcomes of cardiopulmonary resuscitation in a rat model

OBJECTIVE

To investigate the optimal rewarming rate following therapeutic hypothermia in a rate model of cardiopulmonary resuscitation. Both clinical and laboratory studies have demonstrated that mild therapeutic hypothermia following cardiopulmonary resuscitation improves myocardial and neurologic outcomes of cardiac arrest. However, the optimal rewarming strategy following therapeutic hypothermia remains to be explored.

DESIGN

Prospective randomized controlled experimental study.

SETTING

University-affiliated research institution.

SUBJECTS

Twenty-three healthy male Sprague-Dawley rats.

INTERVENTIONS

Four groups of Sprague-Dawley rats were randomized: 1) normothermia group (control), 2) rewarming rate at 2°C/hr, 3) rewarming rate at 1°C/hr, and 4) rewarming rate at 0.5°C/hr. Ventricular fibrillation was induced and untreated for 8 minutes, and defibrillation was attempted after 8 minutes of cardiopulmonary resuscitation. For the 2, 1, and 0.5°C/hr groups, rapid cooling was started at the beginning of cardiopulmonary resuscitation. On reaching the target cooling temperature of 33°C ± 0.2°C, the temperature was maintained with the aid of a cooling blanket until 4 hours after resuscitation. Rewarming was then initiated at the rate of 2.0, 1.0, or 0.5°C/hr, respectively, until the body temperature reached 37°C ±0.2°C. Blood samples were drawn at baseline and postresuscitation of 4, 6, 8, 10, and 12 hours for the measurements of blood gas and serum biomarkers.

MEASUREMENTS AND MAIN RESULTS

Blood temperature significantly decreased in the hypothermic groups from cardiopulmonary resuscitation to postresuscitation 4 hours. Significantly better cardiac output, ejection fraction, myocardial performance index, reduced neurologic deficit scores, and longer duration of survival were observed in the 1 and 0.5°C/hr groups. The increased serum concentration of troponin I, interleukin-6, and tumor necrosis factor-α was partly attenuated in the 1 and 0.5°C/hr groups when compared with the control and 2°C/hr groups.

CONCLUSIONS

This study demonstrated that the severity of myocardial, cerebral injuries, and inflammatory reaction after cardiopulmonary resuscitation was reduced when mild therapeutic hypothermia was applied. A rewarming rate at 0.5-1°C/hr did not alter the beneficial effects of therapeutic hypothermia. However, a rapid rewarming rate at 2°C/hr abolished the beneficial effects of hypothermia.

Perioperative hyperglycemia is associated with postoperative neurocognitive disorders after cardiac surgery

OBJECTIVE

Neurocognitive disorders commonly occur following cardiac surgery. However, the underlying etiology of these disorders is not well understood. The current study examined the association between perioperative glucose levels and other risk factors and the onset of neurocognitive disorders in adult patients following coronary artery bypass and/or valvular surgery.

METHODS

Adult patients who underwent their first cardiac surgery at a large tertiary care medical center were identified and those with neurocognitive disorders prior to surgery were excluded. Demographic, perioperative, and postoperative neurocognitive outcome data were extracted from the Society for Thoracic Surgery database, and from electronic medical records, between January 2004 and June 2009. Multiple clinical risk factors and measures associated with insulin resistance, such as hyperglycemia, were assessed. Multivariable Cox competing risk survival models were used to assess hyperglycemia and postoperative neurocognitive disorders at follow up, adjusting for other risk factors and confounding variables.

RESULTS

Of the 855 patients included in the study, 271 (31.7%) had new onset neurocognitive disorders at follow-up. Age, sex, New York Heart Failure (NYHF) Class, length of postoperative intensive care unit stay, perioperative blood product transfusion, and other key factors were identified and assessed as potential risk factors (or confounders) for neurocognitive disorders at follow-up. Bivariate analyses suggested that new onset neurocognitive disorders were associated with NYHF Class, cardiopulmonary bypass, history of diabetes, intraoperative blood product use, and number of diseased coronary vessels, which are commonly-accepted risk factors in cardiac surgery. In addition, higher first glucose level (median =116 mg/dL) and higher peak glucose >169 mg/dL were identified as risk factors. Male sex and nonuse of intra-operative blood products appeared to be protective. Controlling for potential risk factors and confounders, multivariable Cox survival models suggested that increased perioperative first glucose measured in 20 unit increments, was significantly associated with the onset of postoperative neurocognitive disorders at follow-up (hazard ratio [HR] =1.16, P<0.001) and that women had an elevated risk for this outcome (HR =4.18, P=0.01).

CONCLUSION

Our study suggests that perioperative hyperglycemia was associated with new onset of postoperative neurocognitive disorders in adult patients after cardiac surgery, and that men tended to be protected from these outcomes. These findings may suggest a need for the revision of clinical protocols for perioperative insulin therapy to prevent long-term neurocognitive complications.

RECOVER evidence and knowledge gap analysis on veterinary CPR. Part 7: Clinical guidelines

OBJECTIVE

To present a series of evidence-based, consensus guidelines for veterinary CPR in dogs and cats.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence and quality, and development of consensus on conclusions for application of the concepts to clinical practice. Questions in five domains were examined: Preparedness and Prevention, Basic Life Support, Advanced Life Support, Monitoring, and Post-Cardiac Arrest Care. Standardized worksheet templates were used for each question, and the results reviewed by the domain members, by the RECOVER committee, and opened for comments by veterinary professionals for 4 weeks. Clinical guidelines were devised from these findings and again reviewed and commented on by the different entities within RECOVER as well as by veterinary professionals.

SETTING

Academia, referral practice and general practice.

RESULTS

A total of 74 worksheets were prepared to evaluate questions across the five domains. A series of 101 individual clinical guidelines were generated. In addition, a CPR algorithm, resuscitation drug-dosing scheme, and postcardiac arrest care algorithm were developed.

CONCLUSIONS

Although many knowledge gaps were identified, specific clinical guidelines for small animal veterinary CPR were generated from this evidence-based process. Future work is needed to objectively evaluate the effects of these new clinical guidelines on CPR outcome, and to address the knowledge gaps identified through this process.

Milrinone, a phosphodiesterase III inhibitor, prevents reduction of jugular bulb saturation during rewarming from hypothermic cardiopulmonary bypass

Introduction: Inadequate cerebral oxygen balance during cardiopulmonary bypass may cause neuropsychological dysfunction. Milrinone, a phosphodiesterase III inhibitor, augments cerebral blood flow by direct vasodilatation. We conducted a prospective, randomized study in patients undergoing cardiac surgery with cardiopulmonary bypass to clarify the clinical efficacy of milrinone in the imbalance of cerebral oxygen supply and demand during the rewarming period of cardiopulmonary bypass.

Methods: This is a prospective, randomized and placebo-controlled study. After anesthesia, a 5.5 F fiberoptic oximeter catheter was inserted into the right jugular bulb retrogradely for monitoring the jugular venous oxyhemoglobin saturation (SjO2). Patients were randomly assigned to two groups, one receiving a continuous infusion of milrinone, 0.5 µg/kg/min during hypothermic cardiopulmonary bypass, and the other receiving saline as control.

Results: Milrinone significantly prevented the reduction of the jugular venous oxyhemoglobin saturation at 10 minutes from the start of rewarming compared with the control group, but did not do so from 10 to 20 minutes after rewarming.

Conclusion: Milrinone suppresses the reduction of SjO2 and improves the balance of cerebral oxygen supply and demand during the early rewarming period of hypothermic cardiopulmonary bypass.

Therapeutic hypothermia: benefits, mechanisms and potential clinical applications in neurological, cardiac and kidney injury

Therapeutic hypothermia involves the controlled reduction of core temperature to attenuate the secondary organ damage which occurs following a primary injury. Clinicians have been increasingly using therapeutic hypothermia to prevent or ameliorate various types of neurological injury and more recently for some forms of cardiac injury. In addition, some recent evidence suggests that therapeutic hypothermia may also provide benefit following acute kidney injury. In this review we will examine the potential mechanisms of action and current clinical evidence surrounding the use of therapeutic hypothermia. We will discuss the ideal methodological attributes of future studies using hypothermia to optimise outcomes following organ injury, in particular neurological injury. We will assess the importance of target hypothermic temperature, time to achieve target temperature, duration of cooling, and re-warming rate on outcomes following neurological injury to gain insights into important factors which may also influence the success of hypothermia in other organ injuries, such as the heart and the kidney. Finally, we will examine the potential of therapeutic hypothermia as a future kidney protective therapy.

Effect of olprinone, a phosphodiesterase III inhibitor, on balance of cerebral oxygen supply and demand during cardiopulmonary bypass

Neuropsychological dysfunction with cardiopulmonary bypass (CPB) may be facilitated by inadequate cerebral oxygen balance during CPB. Olprinone, a phosphodiesterase III inhibitor, augments cerebral blood flow by a direct vasodilator effect on cerebral arteries. We conducted the present randomized study in patients undergoing cardiac surgery with CPB to investigate whether olprinone improved the balance of cerebral oxygen supply and demand during the rewarming period of CPB. After anesthesia, a 5.5 F fiberoptic oximeter catheter was inserted into the right jugular bulb retrogradely for monitoring the jugular venous oxyhemoglobin saturation (SjO2), and a probe of transcranial near-infrared spectroscopy was placed over the forehead for monitoring the bilateral regional cerebral oxygen saturation (rSO2). Patients were randomly assigned to 3 groups, and olprinone was administered at 0, 0.2, or 0.4 μg·kg(-1)·min(-1) after establishment of hypothermic CPB. Olprinone significantly prevented the reduction of the SjO2 at 5 and 10 minutes after the start of rewarming, although it did not alter rSO2. Furthermore, there was a minor reduction of the bilateral rSO2 at low doses of olprinone (0.2 μg·kg(-1)·min(-1)). We conclude that olprinone prevents the decrease of the SjO2 at the rewarming period and improves the balance of cerebral oxygen supply and demand during the rewarming period of CPB. In addition, a future extended study may be required to elucidate the effect of low dose of olprinone.

Emergence cerebral oxygen desaturation without hemodynamic compromise in pediatric patients

Background

The regional cerebral oxygen saturation (rSO₂) decreases significantly during ordinary anesthetic recovery in pediatric patients anesthetized with sevoflurane or desflurane. The present study examined the relationship between rSO₂ and the clinical parameters associated with the degree of anesthetic recovery.

Methods

Twelve pediatric patients with American Society of Anesthesiologists physical status 1 were assigned randomly to receive anesthesia with sevoflurane or desflurane. All children underwent general anesthesia for minor surgery. After surgery, the rSO₂, the age-adjusted MAC fraction of anesthetic concentration (F_E), and the bispectral index (BIS) were recorded over a 10-minute period. The correlations between rSO₂ and candidate predictors, such as F_E, BIS, anesthetic, and duration of anesthesia, were analyzed.

Results

All children recovered uneventfully. The lowest observed rSO₂ reached 63% and the maximum decrease in rSO₂ was 24%. The mean blood pressure and heart rate were maintained within clinical ranges. The decrease in rSO₂ correlated positively with the F_E (r = 0.25, P = 0.00) and the duration of anesthesia (r = 0.24, P = 0.01), and inversely with the use of sevoflurane (r = -0.30, P = 0.00).

Conclusions

Despite normal parameters, cerebral desaturation occurred during the emergence of ordinary general anesthesia even without hemodynamic compromise or arterial desaturation. Cerebral desaturation might be associated with the degree of anesthetic recovery and the use of sevoflurane.

Intraoperative hypothermia during vascular neurosurgical procedures

Increasing evidence in animal models and clinical trials for stroke, hypoxic encephalopathy for children, and traumatic brain injury have shown that mild hypothermia may attenuate ischemic damage and improve neurological outcome. However, it is less clear if mild intraoperative hypothermia during vascular neurosurgical procedures results in improved outcomes for patients. This review examines the scientific evidence behind hypothermia as a treatment and discusses factors that may be important for the use of this adjuvant technique, including cooling temperature, duration of hypothermia, and rate of rewarming.

Mechanisms of action, physiological effects, and complications of hypothermia

BACKGROUND

Mild to moderate hypothermia (32-35 degrees C) is the first treatment with proven efficacy for postischemic neurological injury. In recent years important insights have been gained into the mechanisms underlying hypothermia's protective effects; in addition, physiological and pathophysiological changes associated with cooling have become better understood.

OBJECTIVE

To discuss hypothermia's mechanisms of action, to review (patho)physiological changes associated with cooling, and to discuss potential side effects.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

A myriad of destructive processes unfold in injured tissue following ischemia-reperfusion. These include excitotoxicty, neuroinflammation, apoptosis, free radical production, seizure activity, blood-brain barrier disruption, blood vessel leakage, cerebral thermopooling, and numerous others. The severity of this destructive cascade determines whether injured cells will survive or die. Hypothermia can inhibit or mitigate all of these mechanisms, while stimulating protective systems such as early gene activation. Hypothermia is also effective in mitigating intracranial hypertension and reducing brain edema. Side effects include immunosuppression with increased infection risk, cold diuresis and hypovolemia, electrolyte disorders, insulin resistance, impaired drug clearance, and mild coagulopathy. Targeted interventions are required to effectively manage these side effects. Hypothermia does not decrease myocardial contractility or induce hypotension if hypovolemia is corrected, and preliminary evidence suggests that it can be safely used in patients with cardiac shock. Cardiac output will decrease due to hypothermia-induced bradycardia, but given that metabolic rate also decreases the balance between supply and demand, is usually maintained or improved. In contrast to deep hypothermia (<or=30 degrees C), moderate hypothermia does not induce arrhythmias; indeed, the evidence suggests that arrhythmias can be prevented and/or more easily treated under hypothermic conditions.

CONCLUSIONS

Therapeutic hypothermia is a highly promising treatment, but the potential side effects need to be properly managed particularly if prolonged treatment periods are required. Understanding the underlying mechanisms, awareness of physiological changes associated with cooling, and prevention of potential side effects are all key factors for its effective clinical usage.

Therapeutic hypothermia and controlled normothermia in the intensive care unit: practical considerations, side effects, and cooling methods

BACKGROUND

Hypothermia is being used with increasing frequency to prevent or mitigate various types of neurologic injury. In addition, symptomatic fever control is becoming an increasingly accepted goal of therapy in patients with neurocritical illness. However, effectively controlling fever and inducing hypothermia poses special challenges to the intensive care unit team and others involved in the care of critically ill patients.

OBJECTIVE

To discuss practical aspects and pitfalls of therapeutic temperature management in critically ill patients, and to review the currently available cooling methods.

DESIGN

Review article.

INTERVENTIONS

None.

MAIN RESULTS

Cooling can be divided into three distinct phases: induction, maintenance, and rewarming. Each has its own risks and management problems. A number of cooling devices that have reached the market in recent years enable reliable maintenance and slow and controlled rewarming. In the induction phase, rapid cooling rates can be achieved by combining cold fluid infusion (1500-3000 mL 4 degrees C saline or Ringer's lactate) with an invasive or surface cooling device. Rapid induction decreases the risks and consequences of short-term side effects, such as shivering and metabolic disorders. Cardiovascular effects include bradycardia and a rise in blood pressure. Hypothermia's effect on myocardial contractility is variable (depending on heart rate and filling pressure); in most patients myocardial contractility will increase, although mild diastolic dysfunction can develop in some patients. A risk of clinically significant arrhythmias occurs only if core temperature decreases below 30 degrees C. The most important long-term side effects of hypothermia are infections (usually of the respiratory tract or wounds) and bedsores.

CONCLUSIONS

Temperature management and hypothermia induction are gaining importance in critical care medicine. Intensive care unit physicians, critical care nurses, and others (emergency physicians, neurologists, and cardiologists) should be familiar with the physiologic effects, current indications, techniques, complications and practical issues of temperature management, and induced hypothermia. In experienced hands the technique is safe and highly effective.

Induced hypothermia and fever control for prevention and treatment of neurological injuries

Increasing evidence suggests that induction of mild hypothermia (32-35 degrees C) in the first hours after an ischaemic event can prevent or mitigate permanent injuries. This effect has been shown most clearly for postanoxic brain injury, but could also apply to other organs such as the heart and kidneys. Hypothermia has also been used as a treatment for traumatic brain injury, stroke, hepatic encephalopathy, myocardial infarction, and other indications. Hypothermia is a highly promising treatment in neurocritical care; thus, physicians caring for patients with neurological injuries, both in and outside the intensive care unit, are likely to be confronted with questions about temperature management more frequently. This Review discusses the available evidence for use of controlled hypothermia, and also deals with fever control. Besides discussing the evidence, the aim is to provide information to help guide treatments more effectively with regard to timing, depth, duration, and effective management of side-effects. In particular, the rate of rewarming seems to be an important factor in establishing successful use of hypothermia in the treatment of neurological injuries.

Dexmedetomidine during coronary artery bypass grafting surgery: is it neuroprotective?--A preliminary study

BACKGROUND

In the present study, we aimed to determine whether during coronary artery bypass grafting (CABG) surgery, dexmedetomidine has protective effects against cerebral ischemic injury.

METHOD

Twenty-four patients, aged 50-70 years, undergoing CABG surgery were randomized into two groups of 12 patients each: those receiving dexmedetomidine (group D) and those not receiving it (group C). As basal blood samples from arterial and jugular bulb catheters were drawn, dexmedetomidine (1 microg/kg bolus and infusion at a rate of 0.7 microg/kg/h) was administered to patients in group D. Arterial and jugular venous blood gas analyses, serum S-100B protein (S-100B), neuron-specific enolase (NSE) and lactate measurements were performed after induction, 10 min after the initiation of cardiopulmonary bypass (CPB), 1 min after declamping, at the end of CPB, at the end of the operation and 24 h after surgery. Mann-Whitney U- and Wilcoxon's tests were used for statistical analyses.

RESULTS

No significant between-group differences were found regarding arterial and jugular venous pH, PO(2), PCO(2) and O(2) saturations. S-100B, NSE and lactate levels were also similar between groups D and C. During the post-operative period, there were no clinically overt neurological complications in any patient.

CONCLUSION

Cerebral ischemia marker (S-100B, NSE, lactate) patterns were as expected during CPB; however, there were no differences between the groups, which led us to believe that during CABG surgery dexmedetomidine has no neuroprotective effects. Future studies with larger populations are recommended to further establish the effects of this drug.

Cardiopulmonary bypass temperature and brain function

A debate has emerged in recently published studies about the optimum cardiopulmonary bypass temperature for good neurological outcome - warm vs. cold, i.e. normothermic vs. hypothermic. Although many comparative studies have been performed, the results of these studies are inconclusive and are difficult to interpret. Brain function has been studied in terms of neurological and neuropsychological outcome, protein S100beta levels as a marker of brain damage, and cerebral oxygenation using jugular bulb oximetry and near-infrared spectroscopy. The studies produce no conclusive proof of the superiority of warm or cold cardiopulmonary bypass. However, it appears that any degree of bypass hypothermia (< 35 degrees C) may protect the brain. On the other hand, even a slight increase in bypass temperature to > 37 degrees C may cause marked brain injury.

Prevention of Cerebral Hyperthermia During Cardiac Surgery by Limiting On-Bypass Rewarming in Combination with Post-Bypass Body Surface Warming: A Feasibility Study

Cerebral hyperthermia is common during the rewarming phase of cardiopulmonary bypass (CPB) and is implicated in CPB-associated neurocognitive dysfunction. Limiting rewarming may prevent cerebral hyperthermia but risks postoperative hypothermia. In a prospective, controlled study, we tested whether using a surface-warming device could allow limited rewarming from hypothermic CPB while avoiding prolonged postoperative hypothermia (core body temperature <36 degrees C). Thirteen patients undergoing primary elective coronary artery bypass grafting surgery were randomized to either a surface-rewarming group (using the Arctic Sun thermoregulatory system; n = 7) or a control standard rewarming group (n = 6). During rewarming from CPB, the control group was warmed to a nasopharyngeal temperature of 37 degrees C, whereas the surface-warming group was warmed to 35 degrees C, and then slowly rewarmed to 36.8 degrees C over the ensuing 4 h. Cerebral temperature was measured using a jugular bulb thermistor. Nasopharyngeal temperatures were lower in the surface-rewarming group at the end of CPB but not 4 h after surgery. Peak jugular bulb temperatures during the rewarming phase were significantly lower in the surface-rewarming group (36.4 degrees C +/- 1 degrees C) compared with controls (37.7 degrees C +/- 0.5 degrees C; P = 0.024). We conclude that limiting rewarming during CPB, when used in combination with surface warming, can prevent cerebral hyperthermia while minimizing the risk of postoperative hypothermia[corrected].